Our issue was that the special aluminumbottom paint is terrible - lasts maybe 6-9 months when our regular paint often lasts 3 years. That's why we tried the epoxy approach. We're watching our zincs closely but haven't seen a problem yet, & it's been over a year.

Our issue was that the special aluminum bottom paint is terrible - lasts maybe 6-9 months when our regular paint often lasts 3 years. That's why we tried the epoxy approach. We're watching our zincs closely but haven't seen a problem yet, & it's been over a year.

I agree with the concern of using copper based antifouling paint over aluminium. A barrier of 5 coats of epoxy is recommended when useing non copper based antifouling.
Most aluminium boat owners do not feel copper based antifouling is safe no matter how good the barrier is. A saildrive is will develop problems much quicker and more severely than an aluminium hull will.
Non copper based antifoulings are a bit less good, but are improving rapidly. Trilux 33 is much better than Trilux and gives us 2 years in the the warm waters of the Mederteranian.

Lanacote works, but you need to be out of the water to do it properly
Clean the prop absolutely..then heat it with a hit air gun..then oaint heated Lanactoe on...should do 6 mths in temperate waters.
In warm waters it doesn't last
Propspeed lasts well in temperate waters, but since leaving my boat in Fiji where the water is 29-31 degC...oysters grow on it if its not moving
If the prop turns every day or so it seems to last 12 mths
cold galvanising I haven't used...but is zinc a biocide ???...its organic growth thats the issue...

The zinc sprays do absolutely nothing to growth in Long Island Sound. The NY sealife laughs at it. I use Petit Prop Kote on the blades, and Petit Vivid on the hub and shaft. Better results but still needs to be manually cleaned monthly at minimum.

I have never tried zinc sprays. If the zinc coating is eroding I think it would have some effect. Zinc anodes suffer less growth than unprotected surfaces.

I live on the boat at anchor and occasionally, over winter, will anchor in the same spot for weeks at a time. When doing this patrs of the galvanised chain picks up quite a bit of marine growth (where it's not abraded by the bottom). This suggests that the effect of zinc sprays on retarding growth would be small